1. Field of the Invention
The present invention relates generally to a rotating cutter hub and blade assembly used in a pelletizer in which a molten polymer is extruded as strands through orifices in a die plate and the strands are cut into pellets with the cutter blades. In this invention, the cutter blades are generally parallelepiped in cross-section and are mounted on the cutter hub at a steep angle to the die face. The front side or leading edge surface of each blade is beveled to present a blunt, generally perpendicular leading or cutting edge or surface to contact and shear the extruded strands along the die face.
2. Description of the Prior Art
The use of a cutter hub with a plurality of blades mounted thereon in association with the die face of a die plate in an underwater and other pelletizers is well known. U.S. Pat. No. 4,123,207 discloses initial developments of a cutter hub supporting a plurality of replaceable cutter blades having a cutting edge associated with the die face of an underwater pelletizer to cut extruded strands of polymer into pellets in which the cutter hub is supported and rotated by a drive shaft with the die face, cutter hub and associated blades being oriented in a water box. Various subsequently issued patents disclose similar pelletizing structures.
Cutter blades of a rectangular configuration having oppositely inclined cutting edges are commercially available in which the inclination of the opposing blade cutting edge is about 49° to the die face, as illustrated in FIG. 11a. Inclined cutting edges are typically formed on opposite end edges of the blades to enable both end edges to serve as cutting edges in association with the die face of the pelletizer. Blades of this type are mounted on cutter hub arms to support the blades in standardized angular positions with respect to the die face of the underwater pelletizer.
Steep angle cutter hub and blade assemblies with the cutting blades mounted at a preferred angle of about 75° to the die face are disclosed in published U.S. Patent Application No. US 2005-0220920-A1, owned by the assignee of the instant application, and the disclosure of which is expressly incorporated by reference in this specification as if fully set forth herein in its entirety. Published U.S. Patent Application No. US 2003-0102395-A1 also discloses an underwater pelletizer cutter hub with separator bodies or cutting blades mounted on the arms in a generally perpendicular relation to the die face. In this publication, the impact slats or separator bodies can be chamfered on their edge pointing toward the cutoff head. These two prior art configurations are illustrated in FIGS. 11b and 11c, respectively, of the drawings.
These prior art structures, however, fail to provide a cutter hub and blade assembly for a pelletizer in which the cutter blades have a bottom surface contact area that can be adjusted and reduced regardless of blade thickness, that can provide a blunt or generally perpendicular leading edge to shear the extruding strands into pellets, that can be used on existing cutter hubs, and that can more readily seat against the die face, especially already used and slightly worn die faces.